Hydrocarbon feedstocks are typically combusted as a fuel. When these hydrocarbon feedstocks contain sulfur, the combustion of the feedstocks produces a pollutant of the atmosphere in the form of sulfur oxide gases. In the petroleum refining industry, it is often desirable to upgrade sulfur containing oil and fractions like heavy oils and residuum by hydrotreating to reduce the sulfur content of the fractions.
In the hydrotreating process, hydrocarbon feedstocks are contacted with a hydroconversion catalyst in the presence of hydrogen at elevated pressure and temperature. Catalysts used in hydrotreating processes generally comprise catalytically active metals from Groups 6, 9 and 10 of The Periodic Table and are typically supported on a support made predominately of alumina. To achieve desulfurization, typical operating conditions hydrotreating processes have included a reaction zone temperature of 300° C. to 480° C. a pressure of 20 to 200 bar, a hydrogen feed rate of 90 to 2500 normal liters of hydrogen gas per liter (Nl/l) of oil feed, and a catalyst such as nickel or cobalt and molybdenum or tungsten on a predominately alumina support.
In addition to upgrading the heavy oil or residuum stock to reduce sulfur, it is highly desirable to upgrade the hydrocarbon feedstocks to provide a low carbon residue.
Carbon residue is a measurement of the tendency of a hydrocarbon to form coke. Expressed in weight percent, carbon residue may be measured as microcarbon residue (MCR). The MCR content in a hydrotreated residual feedstock is an important parameter since the hydrotreated residue usually acts as feed to a coker or the fluid catalytic cracking (FCC) unit. Decreasing the MCR content in a hydrotreated residue decreases the amount of low value coke generated in the coker and increases the amount of gasoline generated in the FCC unit.
To this end, there remains a need to develop catalyst compositions which provide good hydrodesulfurization of heavy oil and residuum feedstocks while simultaneously providing improved MCR conversion during a hydrotreating process.